Coaxial to waveguide mode-converting duplexer employing nonreciprocal phase shifting means



Aug. 17, 1965 B E 3,201,715

COAXIAL TO WAVEGUIDE MODE-CONVERTING DUPLEXER EMPLOYING NON-RECIPROGAL PHASE SHIF'I'ING MEANS Filed OCt. 25, 1961 5 Sheets-Sheet l ..,2 fl "a,

-FIGB.

TRANSMITTER IN V EN TOR.

MAURICE E. BREESE BY TRANSMITTER M. E. BREESE MODE- Aug. 17, 1965 3,201,715 LOYING COAXIAL TO WAVEGUIDE CONVERTING DUPLEXER EMP NON-REGIPROGAL PHASE SHIFTING MEANS 3 Sheets-Sheet 2 Filed Oct. 25, 1961 INVENTOR.

ATTO IVE) MA (JR/CE E 595555 Aug. 17, 1965 M. E. BREESE 3,201,715 COAXIAL T0 WAVEGUIDE MODE-CONVERTING DUPLEXER EMPLOYING NON-RECIPROCAL PHASE SHIFTING MEANS Filed Oct. 25. 1961 v 3 Sheets-Sheet 3 MA 09/65 5. BREESE BY M- AT;0RNEY 2 United States Patent Ofi ice ihljilh Patented Aug. iii, i965 CGAXIAL WAVEEGUEDE ll'iifillECfiNVllllT- ENG EMPLQYENG NQNRElIlPRO- PHASE TENS IVIEANS M'anrice E, Ereese, Huntington, N.Y., assignor to perry Rand Corporation, Great Neck, N.Y., a corporation of Delaware (8st. 25, 1%1, Ser. No. 147,545 9 Claims. (Cl. 333fl.1)

This invention relates to a duplexing network for use between coaxial and uniconductor waveguides.

The well-known function of a duplexer in a microwave communication or radar system is to connect the transmitter to a radiating antenna and to isolate the receiver from the same antenna during the transmitting portion of the operation and to edect a reversal of said connections during the receiving portion of the operation 50 that only the receiver is connected to the antenna. Quite often the waveguide feeding the antenna is a coaxial transmission line in order to accommodate a rotary joint, while the transmission lines from the transmitting and receiving portions of the system are uniconductor waveguides such as rectangular waveguides. In the waveguide network joining the transmitter and receiver to the antenna, means must be provided for performing the usual duplexing operation and for converting the waves from 'IE rectangular uniconductor waveguide mode to TEM coaxial waveguide mode. Packaging considerations usually require that these functions be performed with equipment which requires as little space as possible, and high power and frequency bandwidth operating requirements dictate that the equipment be as simple as possible so as to avoid excessive bends, twists, constrictions, obstructions etc. which usually limit the power handling and bandwidth capabilities of the system. Accompanying these requirements is the additional practical requirement that the network be relatively easy and economical to construct.

It therefore is an object of this invention to provide a high power and broadband waveguide network for performing a duplexing operation and for converting between rectangular uniconductor and coaxial Waveguides.

Another object of this invention is to provide a coaxialto-uniconductor waveguide transition which is compatible with, and forms part of, a duplexing network.

Another object of this invention is to provide a relatively compact and simple waveguide network for performing a duplexing operation and for converting the transmission line from uniconductor to coaxial waveguides.

Another object of this invention is to provide a waveguide network for performing a duplexing operation utilizing unidirectional phase shifting elements, and to accomplish highpower broadband mode conversion from uniconductor to coaxial waveguide by utilization of the phase relationships established in the duplexing operation, hence achieving both mode conversion and duplexing functions with a minimum of network complexity.

In accordance with this invention, the mode-converting duplexer is comprised of a uniconductor waveguide hybrid junction such as a magic tee or 3 db directional coupler. Differential phase shifting means are coupled to at least one terminal of a pair of terminals of the by 'brid so that the waves propagating in two uniconductor waveguides toward the coaxial waveguide are 180 out of phase with each other, and the difference in phase shift in the two waveguides for opposite directions of wave propagation is 180. The rectangular waveguides coupling the two adjacent terminals of the hybrid are physically positioned contiguous each other with a common board wall therebetween, and an axially-aligned transition section joins the contiguous uniconductor waveguides to a coaxial waveguide. The common broad wall of the uniconductor waveguide tapers into the center conductor of the coaxial line, and the waves in the two uniconductor waveguides being 180 of the phase join on said center conductor to propagate in a TEM mode in the coaxial waveguide. in the reverse direction of propagation, waves propagate from the coaxial line to both the uniconductor waveguides and in passing through the differential phase shifter the phase relationship between the two waves is altered so that they combine in the hybrid junction to propagate from an output terminal that is difierent from the input terminal of said junction.

The present invention will be described by referring to the accompanying drawings wherein:

FIG. 1 is an isometric illustration, partly broken away, showing an embodiment of the invention using a comron broad wall hybrid directional coupler;

FIG. 2 is a series of cross-sectional views at different positions along the structure of FIG. 1 illustrating the electric field patterns at the respective cross sections;

FIG. 3 is an alternative embodiment of the invention wherein the hybrid junction is a common narrow wall hybrid directional coupler;

FIG. 4 is a series of cross-sectional views taken at different positions along the structure of FIG. 3 illustrating the electric field patterns at the respective cross sections;

FIG. 5 is an embodiment of the invention similar to the embodiment of PEG. 1 wherein the hybrid junction is a folded E-plane magic tee;

FIG. 6 is a series of waveforms illustrating the propagating waveforms at different places in the device of FIG. 5;

FIG. 7 is another embodiment of the invention employing a folded l-l-plane magic tee hybrid junction, and;

FIG. 8 is a series of waveforms illustrating the propagating waveforms at various places in the device of FIG. 7.

Referring now to FIG. 1 of the accompanying drawings, the mode-converting duplexer is comprised of a broad wall hybrid directional coupler it) which in turn is comprised of top and bottom adjacent waveguides 11 and 12 which have a common broad wall therebetween. Said directional coupler has one pair of terminals 33 and 1- which may be coupled respectively to the receiver and transmitter, and a second pair of terminals 15 and 16 which respectively are coupled to differential phase shifting sections 21 and 22. Coupling between waveguides 11 and i2 is accomplished in hybrid coupler ltl by means of. coupling slots 13 and 191 in the common broad wall. Hybrid coupler lil may be the type described in US. latent 2,833,933. It is the characteristic of this broad wall hybrid coupler that waves coupled into terminal 14 will be divided evenly by coupling slots 18 and 19 and will propagate with equal magnitudes in primary and secondary waveguides 12, and ll. It is a further characteristic of the broad wall hybrid coupler that waves which propagate straight through the coupler in the primary waveguide will lag by the coupled waves which are coupled into the secondary waveguide.

Diiferen ial phase shifting sections 21 and 22 are the type now well known in the art, and for use in the rectangular uniconductor waveguides illustrated in FIG. 1 will take the form of a transversely magnetized ferrite element asymmetrically positioned in the waveguide. This type of phase shifter is discussed on page 52 and elsewhere in the January 1955 issue of the Bell System Technical Journal. The symbols used in FIG. 1 to denote these dhlerential phase shifters now are common and indicate, for instance, that phase shifter 22 introguide 12 tional 90 in phase with respect to will substantially cancel each other.

duces a 90 phase shift in waves propagating in the bottom guide with respect to waves propagating in the top guide for propagation from left to right in said waveguides. Similarly, diiferential phase shifter 21 provides the 90 phase shift of waves propagating in the top guide with respect to waves propagating in the bottom Waveguidefor propagation from right to left.

The top and bottom uniconductor waveguides 11 and 12 continue through phase shift sections 21 and 22 and .are coupled to axially-aligned uniconductor-to-coaxial transition section 25 wherein the outer conductor 26 allow rotation of a coaxial waveguide antennafeed 33,

this being a common arrangement in many radar systems. In the operation of the mode-converting duplexer of of the waves will be coupled to the transmitter at ter- FIG. 1, microwave energy from a transmitter is coupled into terminal 14, FIG. 2a, and divides evenly at the coupling slots 18 and 19 between primary waveguide 12 and secondary waveguide 11 with a phase relationship such that the waves that propagate toward terminal 16 lag by 90 the waves propagating toward terminal 15, as

- illustrated in FIG. 2b. The respective waves then pass through differential phase shifting sections 21 and 22 and the waves in bottom waveguide section 12 are delayed in additional 90 in phase by phase shifting section 22 so that said waves now are 180 out of phase with respect to the waves propagating in top waveguide 11, as illustrated in FIG. 20. In passing through transition section 25"the waves propagate in a mode illustrated schematically inFIG. 2d, .and upon reaching coaxial line" section propagate in a true TEM mode, FIG. 2e. Said waves then are coupled through rotary joint 32 to antenna 33 and are radiated therefrom.

In the Ie ceiVed'mOde of operation, electromagnetic waves received by antenna 33 are coupled in the TEM mode through rotary joint 32 to coaxial line section 30, FIG.'2e, through transition section 25 in the mode illustrated in FIG. 2d, and into re'ctangular ,uniconductor waveguides 11 and 12 in the modes illustrated in FIG. 20. The respective waves in the two waveguides then pass .through differential phase shifting sections 21 and 22 wherein the waves in the top waveguide 11 are retarded in phase 9O with respect to the waves in bottom waveso that the wave relationship between the respective waves is as illustrated in FIG. 2 wherein the waves in the top waveguide '11 are represented at an angle at 90 and the waves in the bottom waveguide 12 are represented at an angle of 180. In passing through hybrid directional coupler 10 waves passing directly'through top waveguide 11 are retarded an addithe waves in bottom waveguide section 12 so that they now have a total phase "delay of 180 so asto combine in phase with the waves coupled into top waveguide 11 from bottom waveguide 12. These waves then continue on to the receiver which is not illustrated. On the. other hand," waves coupled from top waveguide 11 into bottom waveguide section are at an angle of -90 and the waves passing directly through bottom waveguide section 12 (at a phase angle of 180) experience anadditional 90, phase lag in waveguide 12 combine in destructive interference with the coupled waves from top waveguide 11 and the two Therefore, substantially all received Waves will be coupled from antenna 33 to the receiver at terminal 13 and substantially none minal 14.

From FIG. 1 and the above description it will be seen that the operation of hybrid directional coupler 1i diiferential phase shifters 21 and 22 and transition section 25 are uniquely suited to duplex and simultaneously perform mode conversion between rectangular uniconductor waveguide and coaxial'waveguide, inasmuch as therwave relationship established between Waves in the various sections of the structure are utilized in hoth functions and have significance only in connection with the particular typesv of waveguides employed herein and the particular function's performed. It further may be seen that transition section 25 is an integral part of the duplexerinasmuch asduplexing operation can be accomplished with the device of this invention only with waves having the wave relationships established at said transition section 25. i

, An alternative embodiment of the mode-converting duplexer of this invention is illustrated in FIG. 3 which is similar tothe' embodiment illustrated in FIG. 1 with the exception that the hybrid coupler employed in FIG. 3 is'a common side wall hybrid coupler 49 rather thanthe cornmon'top wall hybrid coupler 10 illustrated in FIG. 1. A distinction in the operation of these two couplers should be noted at this point. In'the common narrow wall hybrid coupler, an example being the type described in US. Patent 2,739,287, the waves coupled into the secondary waveguide lag by 90 the waves which 'progagate directly through the'primary waveguide. This relationship is just opposite to the relationship which exists in the common broad wall hybrid coupler used in the embodiment of FIG. 1.

In the operation of the embodiment of FIG. 3, waves from the transmitter are coupled into terminal 41, FIG.

4a, and propagate to the coupling region of hybrid coupler 40 wherein they divide equally between waveguides 43 and 44 with the, wave relationship illustrated in FIG.

In passing through differential phase shifting sections 45 and 46 the wavesin waveguide section 44 will be retarded an additional 90 with respect'to waves in waveguide 43 so. thatthe Waves in 'the two waveguides now are 180 out of phase with respect to each other, FIG. 40. The two waveguide sections 43 and 44 then are bent so that they are aligned and share a common broad wall in the manner illustrated in FIG. 4d. Transition section 50 is substantially identical to transition section 30 of FIG.

1 and operates in the manner illustrated in FIGS. 4e and 4 to convert the waves into a TEM mode for propagation on coaxial line section 51.

In the received mode of operation the TEM mode waves propagate from coaxial line section 51, FIG. 4

,passing through the coupling section and now are at a phase angle of 270 so that the direct waves in bottom through transition section 50, FIG. 42, and are coupled to rectangular uniconductor waveguides 43 and 44 to propagate therein in TE modes with'a phase difference of 180 with respect'toeach other, FIG. 4d. In passing through differential phase shifting section 45 and 46, Waves in'waveguide 43 are retarded so that the phase relationship between waves in the two waveguides is as villustrated in FIG. 4g. In passing through hybrid directional coupler 40 waves coupled from waveguide 43 into waveguide 44- experience. an additional 90 phase re tardation, va total of combine in phase with the direct waves propagating through waveguide 44 and propagate to the receiver. Waves coupled from waveguide 44.

into waveguide 43 experience a 90 wave retardation, a

total of 270, and combine in destructive interference tially all the received energy is coupled from terminal 53 to the receiver and substantially no energy is coupled from terminal 41. t

The embodiment of the invention illustrated in .FIG.

5 is similar to the embodiment illustrated in FIG. 1, one difference being that a folded E-plane magic tee hybrid junction 55 is employed instead of the hybrid directional coupler ll) in FIG. 1. An additional distinguishing feature is that the differential phase shifter 56 introduces 180 additional phase difference between the waves propagating from right to left in uniconductor waveguides 58 and 59. N phase shift is introduced to waves propagating in the opposite direction in the two waveguides. The structure to the right of diiferential phase shifter 56 is substantially identical to the structure to the right of differential phase shifter 22 of FIG. 1, consequently furthcr description of this additional structure is unnecessary. The folded E-plane hybrid junction of FIG. is of the type described and claimed in US. Patent 2,853,683.

In the operation of the mode-converting duplexer of FIG. 5, waves from a transmitter are coupled into terminal 6G with the polarity indicated thereat, are coupled into junction 55 and are coupled with equal magnitudes into waveguides S8 and 59 with the polarities illustrated in FIG. 5. These waves propagate through the transition system onto the coaxial line section in the manner discussed in connection with FIG. 1. In the receive mode of operation, waves propagate from the coaxial line section, through the transition section and into rectangular uniconductor waveguides 58 and 59 with the relationship illustrated in FIG. 6a. In passing through differential phase shifter 56, the waves in the lower waveguide 58 experience a 180 phase shift so that the relationship between the waves in waveguides 58 and 5% now are as illustrated in FIG. 6b. These waves combine in phase in the junction of magic tee 55 and propagate substantially exclusively to terminal 62. Terminal 60 is substantially isolated from the received waves because of the operation of the folded E-plane magic tee. Thus duplexing operation together with mode conversion between rectangular uniconductor waveguides 5S and 59 and the coaxial waveguide has been accomplished.

A further embodiment of the invention is illustrated in FIG. 7 which is similar to the embodiment illustrated in FIG. 3, with the exception that a folded H-plane magic tee hybrid junction 70 is employed in the place of narrow wall hybrid directional coupler 49 in FIG. 3. Further, a 180 differential phase shifter 71 is employed in FIG. 7 to establish the correct wave relationships for duplexing between waves propagating in waveguides 74 and 75. The folded H-plane magic tee hybrid junction 70 may be of the type described in US. Patent 2,840,787. The portion of the mode-converting duplexer of FIG. 7 which is to the right of difierential phase shifter 71 is substantially identical to the corresponding portion in FIG. 3 and will not be further explained inasmuch as the operation is identical.

In the operation of the device of FIG. 7, waves from a transmitter are coupled to terminal 77 with the polarity indicated thereat, and are coupled through the junction to uniconductor waveguides 7d and 75 with the relative polarities indicated in FIG. 8a. Differential phase shifter 71 has no effect on the waves propagating in the waveguide 75 so that the waves will continue to propagate in waveguides 7S and 76 and will combine in the T EM mode in the coaxial line section in the manner described in connection with FIG. 3. In the received mode of operation, waves are coupled from the coaxial waveguide, through the transition section into waveguides 74 and 75 in the manner previously described in connection with FIG. 3. Upon encountering differential phase shifter 71 the waves in waveguide 75 will be shifted in phase by 180 and the waves in waveguides 74 and 75 will be in phase with respect to each other, as illustrated in FIG. 81;. These waves combine in folded H-plaue magic tee hybrid junction 7;} and propagate from terminal 8i) to the receiver. Because of the operation of the junction, substantially none of the received waves are coupled to terminal 77. Again, it is obvious that a duplexing operation and a simultaneous conversion of propagating modes has been achieved.

It now should be apparent that the axially-aligned arrangement of the hybrid junction, diiferential phase shifter and transition section provides a relatively simple, compact, broadband and relatively high power device for performing the dual function of duplexing and mode conversion between rectangular uniconductor waveguide and coaxial waveguide.

While the invention has been described in its preferred embodiments, it is understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

ii hat is claimed is:

l. A waveguide network for per-forming a duplexing operation bet-ween uniconductor and coaxial waveguides, comprising the combination of a uniconductor waveguide hybrid junction having two pair of terminals, waves coupled int-o either one of the terminals of the first one of said pairs of terminals dividing equally and propagating from both terminals or" the second pair of terminals, two adjacently-positioned uniconduc-tor waveguides having a common broad wall therebetween respectively coupled to the terminals of said second pair of termirials, dir'ferential phase shifting means coupled between at least one of the terminals of said second pair of terminals and its respective adjacently-positioned uniconductor waveguide, the electrical distance from a first terminal of said first pair of terminals to a first One of said uuiconduct or waveguides being 180 longer than the electrical distance to the other one of said uniconductor waveguides for waves propagating in one direction and the electrical distance from the second terminal of said first pair of terminals to the other one of said uniconduct-or waveguides being 180 longer than the electrical distance to the first one of said uniconductor waveguides for waves propagating in the opposite direction, and a uniconductor-to-coaxial waveguide transition section coupled to the end of said two uniconduct-or waveguides, said transition section having a center conductor coupled to the common broad Wall of said two uniconductor waveguides and tapering in width throughout its length substantially to the dimensions of a center conductor of a coaxial waveguide.

2. The combination claimed in claim 1 wherein said hybrid junction is a common bro-ad wall directional coupler having primary and secondary waveguides and wherein said phase shifting means are coupled to both terminals of said second pair of terminals and produce dill'erential phase shift in waves propagating in the primary waveguide with respect to waves propagating in the second waveguide for propagation in one direction and introduce 90 differential phase shift of waves propagatin in the secondary waveguide with respect to waves in the primary waveguide for propagation in the opposite direction.

3. The combination as claimed in claim 1 wherein said hybrid junction is a common narrow wall directional coupler having primary and secondary waveguides and wherein said phase shifting means is coupled toboth terminals of said second pair of terminals and produce 98 differential phase shift in waves propagating in the secondary waveguide with respect to waves in the primary waveguide for propagation in one direction and introduces 90 differential phase shift in waves propagating in the primary waveguide with respect to waves propagating in the secondary waveguide for propagation in the opposite direction.

t. The combination claimed in claim ll wherein said hybrid junction is a folded E-plane magic tee and wherein said phase shifting means is coupled to only one terminal of said second pair of terminal and introduces 180 diiferential phase shift in waves propagating in one waveguide. V

'5. The combination claimed in claim 1 wherein said hybrid junction is a folded H-plane magic tee and wherein said phase shifting means is coupled to only one terminal of said second pair of terminals and produces 180 differential phase shift in waves propagating in one waveguide.

'6. An axially-aligned waveguide network for performing a duplexing operation between uniconductor and coaxial waveguides comprising the combination of a uni conductor waveguide hybrid junction having two pairs of terminals, waves coupled into either one of the termin-alsof the first one of said pairs of terminals dividing equally and propagating from both terminals of the second pair of terminals, two adjacently-positioned uniconduct-or Waveguides having a common broad wall therebetween and respectively coupled to said second pair of terminals, uniconductor waveguide differential phase shifting means coupled between at least one of the terminals of said second pair of terminals and its respective adjacently-positioned uniconductor waveguide, the difierential phase shift introduced to waves propagating in opposite directions through said phase shifting means being 180, and an axially-aligned uniconductorto-coaxial waveguide transition section coupled to the end of said two uniconductor waveguides, said transition section having a center conductor coupled to the common broad wall of said two uniconductor waveguides and tapering in width throughout its length substantially to the dimensions of a center conductor of a coaxial waveguide.

7. A mode-converting duplexer coupled between a coaxial waveguide and two uniconductor waveguides comprising a uniconductor waveguide hybrid junction having two pairs of terminals, said junction operating to divide 7 equally between two terminals of one pair of terminals the waves coupled into one terminal of the other pair of terminals, a pair of uniconductor waveguides sharing a common broad wall therebetween and respectively coupled to the terminals of said one pair of terminals, differential phase shifting means coupled between at least one of the terminals ofsaid one pair of terminals and its respective adjacently-positioned uniconductor waveguide, the' difference in electrical distance between the paths traveledby Waves propagating in one direction between one terminal of said one pair of said terminals and the two uniconductor waveguides being 180 and the difierence in electrical distance between the paths traveled by waves propagating in theopposite direction between the other terminal of said one pair and the two uniconductor waveguides being 180, a coaxial waveguide having inner and outer conductors, and a transition section between said coaxial waveguide and said two uniconductor waveguides, said transition section having first and second pairs of terminals, the terminals of said hybrid junction being related so that Waves coupled 6 into either one of the terminals of said first pair of teranimals will divide equally between the two terminals of the second pair of terminals, first and second rectangular uniconductor waveguides respectively coupled to the terminals of said second pair of terminals, said two Q rectangular .uniconductor waveguides being substantially aligned with respect to said hybrid junction and being adjacently-positioned at their ends oppositevsaid hybrid junction with a common broad wall therebetween, dif-- tapering along its length to a center conductor of a coaxial waveguide.

9. A mode-converting duplexer for coupling between a coaxial waveguide and two uniconductor Waveguides comprising a uniconductor hybrid directional coupler having a first pair of adjacently-positioned terminals'for coupling to said two uniconductor waveguides, first and second differential phase shiftingmeans coupled respectively to each of a second pair of adjacently-positioned terminals of said directional coupler, said first differential phase shifting means introducing a 90 phase shift to waves propagating'in a first direction with respect to waves propagating in the opposite direction and the second differential phase shifting means introducing a 90 phase shift to waves propagating in said opposite direction with respect to waves propagating in said first direction, two axially-aligned rectangular uniconductor wave-' guide means coupled through said. phase shifting means to said second pair of adjacently-positioned terminals of said directional coupler, said two rectangular uniconductor waveguides being adjacently positioned attheir ends opposite said directional coupler and having a common broad wall therebetween, said phase shiftingmeans cooperating with said directional coupler tocouple waves from one terminal of said first pair ofterminalsinto the respective rectangular uniconductor waveguides with a phase relationship of 180.with respect to each other, an axially-aligned uniconductor-to-coaxial waveguide transition means coupled at one end to said two adjacent-' ly-positioned rectangular uniconductor waveguides and having an inner conductor connected to said common broad wall and tapering along its length to a center conductor of a coaxial waveguide, and an axially-aligned coaxial waveguide coupled to the oppositeend of said transition section, whereby waves coupled 1 to one terminal of said first pair of terminals propagate through said directional coupler, through said phase shifting means and said transitionsection and combine to propagate in said coaxial waveguide in a TEM mode.

References Cited by the Examiner. UNITED STATES PATENTS 2,739,287 7 3/56 Riblet 33311 2,816,271 12/57 Barker 333-13 2,833,993 5/58 Riblet 3331O 2,840,787 6/58 Adcock 33311 2,853,683 9/58 Murphy 333*11 2,923,897 2/60 Lowhurst 333-21 2,973,512 f 2/61 Walsh 33.3-24.1 3,036,278 5/62 Chait et al. 333-,-1.1

HERMAN KARL SAALBA'CH, Primary Examiner. 

1. A WAVEGUIDE NETWORK FOR PERFORMING A DUPLEXING OPERATION BETWEEN UNICONDUCTOR AND COAXIAL WAVEGUIDES, COMPRISING THE COMBINATION OF A UNICONDUCTOR WAVEGUIDE HYBRID JUNCTION HAVING TWO PAIRS OF TERMINALS, WAVES COUPLED INTO EITHER ONE OF THE TERMINALS OF THE FIRST ONE OF SAID PAIRS OF TERMINALS DIVIDING EQUALLY AND PROPAGATING FROM BOTH TERMINALS OF THE SECOND PAIR OF TERMINALS, TWO ADJACENTLY-POSITIONED UNICONDUCTOR WAVEGUIDES HAVING A COMMON BROAD WALL THEREBETWEEN RESPECTIVELY COUPLED TO THE TERMINALS OF SAID SECOND PAIR OF TERMINALS, DIFFERNETIAL PHASE SHIFTING MEANS COUPLED BETWEEN AT LEAST ONE OF THE TERMINALS OF SAID SECOND PAIR OF TERMINALS AND ITS RESPECTIVE ADJACENTLY-POSITIONED UNICONDUCTOR WAVEGUIDE, THE ELECTRICAL DISTANCE FROM A FIRST TERMINAL OF SAID FIRST PAIR OF TERMINALS TO A FIRST ONE OF SAID UNICONDUCTOR WAVEGUIDES BEING 180* LONGER THAN THE 